Bonding metals with explosives



Aug. 20, 1968 ."o. R. BERGMANN ET AL 3,397,444

. BONDING METALS WITH EXPLOSIVES 4 Filed Oct. 23, 1965 2 Sheets-Sheet 1 FIG.

INVENTORS Qs'wAw R. Elks/74ml 6:00;; )8 COMM Ammo #A azrzm/v Aug. 20, 1968 o. BERGMANN ET AL 3,397,444

BONDING METALS WITH EXPLOSIV-ES;

Filed Oct. 23, 1965 2 Sheets-Sheet 2 e= 24.? o 2000 2 sec 0:5600 777/556 0/250 770 OF amt/W770 INVENTORS OS- WALD R. BERGMNN GEORGE R. COWAN ARNOLD H. HOLTZHAH United States Patent 3,397,444 BONDING METALS WITH EXPLOSIVES Oswald R. Bergmann, Cherry Hill Township, George R.

Cowan, Woodbury, and Arnold H. Holtzman, Cherry Hill Township, N.J., assignors to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Filed Oct. 23, 1965, Ser. No. 503,261 12 Claims. (Cl. 29470.1)

ABSTRACT OF THE DISCLOSURE Metals are explosion bonded by being driven together progressively with an explosive at a low collision velocity at Which bonded products having relatively little melt and improved physical properties are obtained.

This invention relates to an improved process for cladding metals by means of explosives, and to improved clad products obtained thereby.

US. Patent 3,137,937 and copending, ce-assigned U.S. patentapplication Ser. No. 217,776, now Patent No. 3,- 233,312 describe a process for producing metallurgically bonded clad products by means of explosives. According to the process described, the metal layers to be metallurgically bonded together to form the clad product are positioned substantially parallel to one another and spaced apart a distance of at least 0.001 inch, and a layer of detonating explosive on the outside surface of at least one or the metal layers is initiated so that detonation is propagated parallel to the surfaces of the metal layers. The metal layer adjacent the explosive is propelled toward the other metal layer, collides with it, and is bonded thereto metallurgically. An essential condition of the described process is that the detonation velocity of the explosive be less than 120% of the velocity of sound in that metal in the system having the highest sonic velocity. The minimum detonation velocity set forth is about 1200 meters per second, this velocity being about the lowest at which commonly available explosives are found to propagate detonation reliably.

The above-cited patent and application show by way of detailed working examples the use of explosives having detonation velocities ranging from 3900 to 5000 meters per second. Such explosives in combination with the other process parameters outlined, afford strong continuously and metallurgically bonded (as opposed to mechanically bonded) clad products wherein the bond is substantially dilfusionless and there are present regions, substantially homogeneous in composition, of alloy of the bonded metals. This alloy, which is solidified melt, is present either as a continuous layer between the bonded metals, or as a plurality of periodically spaced islands or regions separated by direct metal-to-metal metallurigical bonding. In the case of the continuous-layer type of bond, the general contour of the interface is substantially straight or irregularly curved, while in the case of the type of bond having alloy in periodically spaced regions, the interface between the bondedmetals usually has a wavy contour.

Another explosion-bonding process is described in Belgian Patent 633,913. The process of the Belgian patent involves initially disposing the metal layers to be bonded at an angle to one another, positioning a layer of explosive adjacent the outer surface of 'at least one of the layers, and then detonating the explosive to drive the layers together.

It has now been found that under a certain specific narrow range of conditions within both of the aforementioned general processes, but preferably within the scope of the aforementioned explosion-bonding process described in US. Patent 3,137,937, there are obtained products having a unique combination of excellent strength, ductility, and freedom from solidification defects.

The process of this invention is an improvement in the process for metallurgicaly bonding layers of metals by propelling the layers together with an explosive, said improvement comprising effecting collision with respect to each of said metal layers at a velocity of about from 1400 to 2500 meters per second and below 120% of the sonic velocity of the metal in the system having the highest sonic velocity, the surfaces to be bonded of said layers being disposed at an angle of less than 10 to each other prior to detonation of said explosive.

The collision velocity is the velocity with which the line or region of collison travels along the metal layers to be bonded.

The unique and preferred products of this invention are multi-layer composites comprising at least two, and preferably two or three, metallic layers bonded together, adjacent layers in said composite being of different composition and metallurgically bonded over at least 90% of the interface therebetween, as-bonded, by a substantially diffusionless bond, said composite exhibiting ordered plastic deformation in a direction substantially parallel to said interface localized in the metal bounding each side thereof, any solidified melt present at said interface being present in localized regions between said layers and spaced between areas of metal-to-rnetal metallurgical bonding at said inter-face, said solidified melt having an equivalent melt thickness of less than one micron. As illustrated in the examples, the products of this invention have improved ductility reflected in a percent elongation of the composite, determined in accordance with ASTM designation E8, preferably of at least of the least ductile layer before bonding. Although products of this invention may contain regions of the alloy characteristic of explosion-bonded products generally, in all cases the amount of alloy is substantially less than that obtained heretofore and in some cases may not be observable at a magn'iture of 250x.

In accordance with this invention it has been found that as the collision velocity is decreased a critical velocity occurs below which the bonds change markedly even through all process variables except collision velocity are held constant. In addition, the efiect of process variables differs significantly depending on whether the collision velocity is above or eblow the critical value. Although the critical velocity varies somewhat with the metals being clad, it is below about 2500 1m./sec., and usually between 2300 to 2500 m./sec.

In the collision velocity region above the critical, the amount of solidified melt associated with the bond zone increases 'with collision velocity at any given impact angle (i.e., angle between metal layers on collision); also, when the interface is wavy, the wave amplitude is controlled by impact angle, increasing greatly with said angle. On the other hand, in the velocity region below the critical, there is little or no melt observable at 250x associated with the bond zone regardless of the impact angle, and the wave amplitude for a given metal system is significantly smaller than that produced at the same impact angle at a collision velocity above the critical. Thus, operating in the below-critical region permits the obtaining of consistently low-melt products over a broad range of liquid angle, i.e., a broad range of initial stand-01f distances or initial angles between layers. Also, with a wavy interface, smaller-amplitude waves are obtained in a given system according to the present process. Extremely large wave amplitudes are undesirable when one or more layers of the clad composite are thin since the surface contour of the composite may be affected. Below 1400 m./sec. except with abnormally high explosive loadings and/ or stand-off distances, the products are not as strong as those obtained by the present process.

In the clad products formed by the present process, there is strong metallurgical bonding of the metal layers, substantially all of the bond being of the direct metal-tometal type, that is, greater than 90% of the interfacial area between the metals being bonded is bonded by metalto-metal bonding. Depending on the conditions used in the preparation of the clad product, e.g., the specific collision velocity and impact angle employed, the interface between the metallic layers can be in the form of a substantially straight line or in the form of a wave having a preferably uniform amplitude and wave length. Under most conditions, the wavy bond is formed. Any solidified melt which is present at the interface is present in isolated regions of such size that when the melt therein is converted into an equivalent continuous layer of uniform thickness along the entire interface, said layer is less than about ten microns, and usually less than one micron, thick. Stated differently, the total volume of melt divided by the area of the bonded interfaces is less than microns, and preferably less than 1 micron. This equivalent melt thickness can be conveniently measured by taking a section through a sample parallel to the direction of detonation during bonding, measuring the total area of the melt in the section, and dividing such area by the length of the bonded interface. Clad products made by the present process and having at the interface an amount of melt which, when converted into an equivalent layer of uniform thickness along the entire interface, gives a layer less than one micron thick are preferred and unique products of this invention having particularly outstanding resistance to mechanical stresses. Such clad products having the wavy type of bond interface are preferred in many situations because of their normally higher strength. In addition to providing an improved freedom from solidification defects, the present process also affords im proved product workability, such as formability. Also, the ductility is relatively insensitive to changes in impact angle. Ductility of product is highly desirable in clad composites which are to be worked into various shapes.

Ordered plastic deformation of the metal bounding the interface between metal layers, as used herein with respect to the products of this invention, refers to regular gross plastic deformation in a general direction substantially perpendicular to the collision front occurring during the preparation of the products, i.e., in the direction of the collision, and generally parallel to and localized near the interface. The deformation follows the contour of the interface, e.g., in the case of wavy interfaces it follows the general contour of the waves, and is either precisely parallel to the interface or at some small acute angle thereto, e.g., 10-20. As shown by the arrows in FIGURE 2, the aforementioned deformation is in a general direction away from a point or line in the composite. Stated differently, the arrows show plastic deformation in which the metal flow has been in the general direction of the detonation or collision during the bonding process, that is, deformation in the general direction away from the point or line of initiation of the explosive used in the bonding process. The plastic deformation is concentrated in the region adjacent the interface usually to a depth on either side thereof of less than about 25% of the thickness of the thinner layer bonded at said interface, the depth of deformation in the case of a wavy interface being measured from a plane passing midway between the crests and troughs of the wave and normally being less than about 3 times the wave amplitude on either side of said plane.

Although as illustrated in the figures, the products are usually viewed in cross-section'parallel to the direction of detonation, and, hence, an'y'ofthe aforementioned melt appears as two-dimensionalpockets, in realityany regions of solidified melt are elongated ,zones running parallel to the detonation front. The aforementioned melt, if observable, has a composition between that of the two layers between which it is disposed and the composition thereof is substantially homogeneous throughout each such region. The products are substantially diffusionless throughout in the as-bonded condition; that is, in the as-bonded condition the interface and adjacent areas, including the prodminant metal-to-metal bonded regions as well as the alloy regions, if any, exhibit no gradient composition charactertistic of diffusion-bonded products. Preferably, in the as-bonded condition they show no diffusion across any interface. when measured with an electron probe and sectioning techniques having a limit of resolution of 0.2 micron. Especially preferred products are also characterized by a shear strength, measured parallel to the interface and substantially perpendicular to any waves therein, of at least about that of the parent metals before cladding. Any interfacial waves usually have an amplitude of about from 5 microns to 0.5 inch and normally no larger than about 50% of the thickness of the thinner layer bonded at the interface, and are substantially uniform in size throughout the composite. Such uniformity, which is a characteristic of the aforementioned preferred embodiment employing a layup having layers to be bonded in substantially parallel alignment, leads to particularly good uniformity of mechanical properties.

For a more complete understanding of the invention, reference is now made to the attached drawings wherein FIGURE 1 is a cross-sectional view of an assembly which can be used to practice the present invention;

FIGURE 2 is a photornicrograph (magnification of 76) of a novel product of this invention showing the unique structure of the bond zone; and

FIGURES 3, 3A, and 3B are photomicrographs of clad products made at three different collision velocities.

In FIGURE 1, metal backer plate 1 and metal cladder plate 2 are parallel to one another and spaced apart so as to provide a stand-oflt 3. The stand-off spacing 3 can be conveniently maintained by metal ribbons 4 such as those described in US. Patent 3,205,574, the ribbons being positioned at the plate corners. A layer of a granular explosive 5 having a detonation velocity of about from 1400 to 2500 meters per second, held in container 6, e.g., made of cardboard, is adjacent the surface of metal layer 2 opposite the surface thereof facing metal layer 1. Explosive layer 5 extends beyond the parallel plate assembly and over metal strip 2a of the same composition and thickness as cladder plate 2. The metal strip and extension of the explosive layer are not critical to the process but provide added assurance that good bonding is achieved at the edge of the plates nearest the explosive initiation point. Explosive layer 5 is initiated by electric blasting cap 7 having lead wires 8 leading to a source of electricity. Upon initiation of explosive layer 5, plate 2 is propelled against plate 1 and collides progressively therewith as the detonation progresses through layer 5, the collision velocity being equal to the detonation velocity of explosive layer 5.

The photomicrographs shown in FIGURES 2, 3, 3A, and 3B are obtained on explosion-clad products described in the examples which follow, and the figures are described more fully therein.

In the improved cladding process of this invention, the metal layers collide at a collision velocity which is in the region below the critical velocity described above, i.e., below about 2500 meters per second; Of two metal layers to be bonded, one may be propelled against the other, stationary, layer or both layers may be propelled toward each other to cause collision. Of three metal layers to be bonded, one metal layer may be propelled toward a second metal layer, which in turn is driven toward a third layer; or two outside layers can be propelled simultane ously toward an inside stationary layer. In like manner, with more than three layers, one or both outside layers can be propelled to cause collision and bonding. The metal layer or layers are propelled by the detonation of a layer of explosive or by another metal layer which is in turn propelled by detonation of a layer of explosive. The layers to be bonded can be arrayed initially parallel to, and spaced apart from, each other, or at some angle to one another. In either arrangement, the controlling parameters are so chosen that the collision velocity is about from 1400 to 2500 meters per second. i

The collision velocity, as has been mentioned above, is the velocity with which the collision region travels along the metal layers to be bonded. More precisely, for two colliding layers 1 and 2, there are two collision velocities, V and V denoting the velocities of the collision region relative to metal layers 1 and 2, respectively, that is, the velocities with which each of the two layers moves into the collision region or, stated differently, the velocities with which points on the inner surface of each of the layers approach the collision region. In most cases described herein the two velocities are the same or substantially the same; hence, there is little difference whether the velocities are considered as one or not. However, unless otherwise indicated, collision velocities of all layers being bonded must be within the indicated values.

In the preferred case of metal layers arrayed substantially parallel to one another, as in Us. Patent 3,137,937 cited above, the layer of explosive is initiated so that detonation is propagated substantially parallel to the surfaces of the metal layers. If there is a layer of explosive adjacent only one of the metal layers, or if an explosive layer of the same detonation velocity is adjacent both metal layers and the explosive layers are initiated simul taneously at corresponding points or lines thereon, the collision velocities relative to both metal layers are equal to each other, and equal to the detonation velocity of the explosive. Thus, this embodiment of the present process employs explosives detonating at a velocity below about 2500 meters per second. I i The explosion cladding of metal layers arrayed initially at an angle to one another is described in detail in Bel: gian Patent 633,913. Usually this angle should be less than 10 and preferably less than 5. As explained therein, the parameters which affect the collision velocities differ depending on the manner of initiation of the explosive layer(s). When a layer of explosive on the external surface of one or of both metal layers is initiated simultaneously over it entire surface the collision velocities of the metal layers are functions of the initial angle 6 between the layers and their velocities V and/or V the vector sum of which, V is the velocity with which the metal layers are propelled toward one another. These relationships are:

Thus, for this arrangement the present process requires 6. that the initial angle between the metal layers and the explosive loading (which affects the velocities of the propelled layer(s) must be adjusted to provide a V and V of less than about 2500 meters per second.

The above-mentioned Belgian patent also teaches that when a layer of explosive on the external surface of one or both metal layers is initiated at a point or along a line the collision velocities of the metal layers are functions of the initial angle 6 between the metal layers; the angles 71 and/or 72 by which the metal layer(s) are deflected by thedetonation pressure; the angle A which is the angle between the initial line of intersection of the planes of the metal plates and any line on the plates along which detonation is propagating; and the detonation velocity D of the explosive. Thus, in addition to the initial angle and explosive loading (on which 7 and 72 'depend), the method or location of the point or line of initiation and the detonation velocity of the explosive-must be adjusted to provide a V and V of less than about 2500 meters per second. Relations for calculating V and V in these situations are (1), (m), (n), and (p) of the cited Belgian patent. Where a single layer of explosive is used:

D sin antitan "n/2 tan 6 sin A] sin 71 sin A cos A 003 A Sin 'Y1+00S 'y tan 5 sin A- I [1t;an /2 tan 6 sin A] sin 71 cos A sin A cos A cos 6 [1+cot 7] tan 5 sin Ac0s A] Where explosive layers are positioned adjacent the external surface of both plates;

sin antitan cos A Deflection angles 71 and'y can be measured in the same manner as plate velocities. One such method for measuring the velocity of an explosively propelled metal plate involves the use of electrical contact pins as is described by D. Bancroft, et al., Journal of Applied Physics, 27, (3) 291 (1956). An optical method is described by W. A. Allen and C. L. McCrary in Review of Scientific Instruments, 24 (2), (1953) and by W. A. Allen, Journal of Applied Physics 24, (9), 1180 (1953); and a method involving use of flash X-radiographs is described A. S. Balchan, ibid. 34, (2), 241 (1963). Also:

V 1=2D sin 7 /2 (or Vpz=2D Sin The angles 6 and 6 are solutions to the equations:

i a +a =a cos 6 (1+cot'y tan 6 sin Acos A) cos 8 (1+cot w -tan 6 sin A-cos A) operating at higher than about 2500 meters per second. In particular, operation in the velocity regionof this in vention yields a low-melt bond zone and higher product ductility over a Wide range *of conditions, thus assuring product integrity under diverseconditions encountered in manufacture and processing-For optimumproperties, reliability and reproducibility, collision velocities of- 1900 to 2300 meters per second are preferred. For any explosion cladding system, the occurrence of strong metallurgical bonding over a large proportion of the interface, is dependent not only on meeting the collision velocity requirement described above but alsoon. the achieving of a certain minimum angle between metal layers on impact. For a given cladding system, operation in the collision velocity range of this invention appears to require a somewhat larger minimum impact angle than does operation in the above-2SOO-meters-per-second region. The larger impact angle can be produced by a larger initial stand-off or angle betweenlayers or 'by use of a larger explosive load. Although the minimum impact angle varies from metal to metal, being about 4 for-cladding systems containing nickel layers and 7 for titanium layers, generally it is in the range of 4 to 10. In any case, an angle of 10 is usually adequate, the precise minimum being established by varying the standoff, initial angle, or load. By way of example, for preferred systems involving layers consisting essentiallly of titanium or nickel (i.e., the indicated metals alone or alloys thereof with minor amounts of alloying elements) the impact angle is preferably about from 7 to and 4 to 18, respectively.

Standoff, loading and initial angle can be varied as indicated within the broad teachings of U8. Patent 3,137,- 937, Belgian Patent 633,913, and US. Ser. No. 217,776 which are incorporated herein by reference; however, each of these interrelated variables are adjusted to optimize results with each particular system. In general, with the preferred technique employing layers in substantially parallel arrangement, point or line initiation and explosive on one or both sides of the layup, loading weights of about 0.2 to 3 times the driven or cladder layer weight are used, while standoifs of about from 0.3 to 0.7 of the cladder layer thickness are employed. Also, in general, explosive loading increases with the mass per unit area and standoff of the driven layer and usually is such that the driven layer has a velocity at collision of at least about 130 meters per second.

The explosive compositions useful in the present process vary widely and the selection of a particular composition will be made on the basis of such factors as the metal layer arrangement employed, ease of handling, economics, etc. In the preferred parallel cladding technique according to this invention, explosive compositions which detonate at velocities below about 2500 meters per second are employed. Typical of such compositions are nitroguanidine in low bulk densities, self-supporting explosive sheet such as the fibrous felt-like compositions described in US. Patent 3,102,833, e.g., PETN and RDX sheets, and a number of permissible explosives such as some of those listed in the US. Bureau of Mines Information Circular 8087 (1962). When the angle cladding technique is employed, explosives having higher detonation velocities can be used, since the required collision velocity can be achieved with explosives of any higher detonation velocity by increasing initial angle (up to 10) and/ or explosive load.

The improved explosion cladding process of this invention is applicable to a wide variety of metals including, for example, aluminum, iron, titanium, columbium, chromium, tantalum, cobalt, nickel, vanadium, zirconium, silver, platinum, copper, gold, as well as alloys of a major proportion, e.g., 50% by weight or more, of one or more of the aforementioned metals with minor amounts of alloying elements. Metals having a specific gravity of at least 2, and preferably about from 4 to 17, particularly copper, nickel, iron, silver, titanium, zirconium, tantalum, and alloys ofthese metals are preferred. The alloys usually contain up to 50%, and preferably up to 30%, of alloying elements. In tantalum, titanium, and zirconium clads, usually the amount of alloying elements is minor, e.g., less than 5%. Preferably, the difference in specific gravity between the metal layers being bonded is no greater than 9. Of course, for practical .purposes, the layers should be sufficiently ductile (e.g., percent elongation of greater than 5%) so that they donot crack or fracture during the bonding process. In general, if a relatively brittle layer is to be bonded to a more ductile layer, explosive is positioned adjacent the more ductile layer and the more brittle layer is used as the backer. While the present process is employed to advantage in .a number of metal systems, it affords particularly improved products in the case of metal systems which form brittle intermetallic phases, e.g., titanium-steel, zirconium-steel, tantalum-steel, and titanium-aluminum.

The technique employed to initiate the explosive layer(s), support the cladding assembly, prepare the metal surfaces, and other-wise effect the bondingprocess are described in the aforementioned patents, the disclosures of which are incorporated herein by reference. A particularly effective means of maintaining the stand-off distance in the parallel technique is that shown in FIGURE 1, and described in detail in US. Patent 3,205,574. The manner of positioning of the assembly is not critical, e.g., a plate assembly can be positioned with the plate farthest from the explosive resting on the ground or on a support material on or in the ground. In some instances, it is convenient to position the assembly so that the plates are standing on their edges.

The process of this invention can be used to produce mill products, i.e., plates, sheets, strips, rods, bars, tubing, etc., comprised of at least two metallic layers of different composition bonded together'over a large portion of the interface between the layers, e.g., over at least of the interface, to form a composite system. The layers of different composition can be two layers of different substantially pure metals; two layers of different alloys (of the same or different metals); or' one layer of a'subs'tantially pure metal and a second layer of an alloy (of the same or a different metal than the first layer). Also, the product can be a composite of two or more layers bonded to a layer of substantially homogeneous composition; or of two or more multilayered composites bonded together. Mill product denotes here a product having a minimum significant dimension of three inches, e.g., a three-inch-long strip, rod, bar, or tube; and a plate or sheet having a length and width of at least three inches.

'The following examples serve to illustrate specific embodiments of the present invention. However, they will be understood to, be illustrative only and not as limiting the invention in any manner.

In all cases the metal surfaces are prepared by abrading with a disc sander and degreasing with alcohol.

The collision velocity given is the approximate detonation velocity of the explosive as measured from framingcamera sequences using a reflected grid-displacement technique, as are the plate velocity and plate impact angle. Such a technique is described by W. A. Allen and C. L. McCrary in Review of Scientific Instruments, vol. 24, pp. -171 (1953). The equivalent melt thickness is the total area of isolated pockets or regions of melt at the interface, in an illustrative cross-section parallel to the direction of detonation, divided by the length of the interface.

Example 1 A nickel plate is clad explosively to a steel plate employing the general arrangement depicted in FIGURE 1. The backer plate 1 is a 7 x 9 inch Grade 1008 steel plate /2 inch thick, and the cladder plate 2 is a 7 x 9 inch Grade A nickel plate /8 inch thick. Grade 1008 steel is a low-carbon or mild steel (about 0.08% carbon); The extension strip is a 1 x 7 inch strip of Grade A nickel /s inch thick. The layer of explosive is a 7'0/30 nitrog-uanidine/corn meal mixture in a loading of 15.4 grams per square inch. The collision (detonation) velocity is 2000 meters per second. The stand-off distance between plates is 156 mils. yOn detonation of the explosive, the plate impact angle is about 7.

After detonation of the explosive, a specimen is cut out of the resulting well-bonded composite for metallographic examination of the bond zone. The interface is wavy and greater than 90% metallurgically bonded, and the equivalent melt thickness is less than 1 The product shows plastic deformation in the metal adjacent the interface in the direction of detonation.

If the procedure above is repeated using a silver plate of like size instead of the nickel above as the cladder layer, substantially similar results are obtained.

plosive. The collision velocity and other fundamental process variables, i.e., cladder plate velocity and plate angle at impact, which prevail under the conditions of each experiment, are determined from framin -camera sequences of the moving cladder plate. The conditions employed and results are summarized in Table I.

In all examples, bonding is effected over greater than 90% of the interface between plates. 7

The general direction of plastic metal flow near the bond zone in the clad products made according to the process of this invention is consistently away from the point or line at which the explosive has been initiated, or, in other terms, away from the center of curvature of a wave front emanating from the initiation point. This is seen in FIGURE 2, which is a photomicrograph (76X magnification) made from the nickel-steel clad product of Example 7b. The direction of plastic flow is indicated by the arrows.

TABLE I.NICKEL-STEEL CLADS Collision Stand-O11, 'Plate Velocity, Plate Impact Bond Zone Characteristics Example N0. Velocity, mlls n1./sec. Angle, Equivalent m./sec. Type Wavelength, ,u Amplitude, p Melt Thick,-

ness, 1.:

1, 650 45 215 7. 4 Srtalght and wavy. 112 10 1 2, 000 45 250 7. 0 Wavy 103 11 1 Example 2 Example 8 The procedure described in Example 1 is used to explosively clad titanium 0/8 inch) onto Grade 1008 steel /2 inch). Grade -A titanium is used for the cladder plate and extension strip. The explosive loading is the same, the collision velocity is again 2000 meters per second, the stand-off distance between plates is 250 mils and the impact angle is about 1l12. The composite is well-bonded over greater than 90% of its interface, and-has a wavy interface. The equivalent melt thickness is less than 1,u., and the product shows plastic deformation adjacent the interface in the direction of detonation, primarily in the area Within inch from the interface on each side. v Inall of the following examples, the detonation velocity can be decreased by increasing the amount of corn meal in the nitroguanidine/corn meal mixture, and increased (to the velocitiesin the range below 3000 meters per second) by decreasing or eliminating the corn meal. For obtaining detonation velocities above 3000 meters per second, the explosive compositions described in US. Patent 3,102,833 canbe used, the disclosure of that patent being incorporated herein by reference. As in the preceding examples, the explosive loading is such that the ratio of theweight of the mixture to the weight of the cladder plate is in the range of 02-3, the precise amount of explosive used being determined by adjusting the loading to give the indicated impact angle.

Examples 3-7 In these examples the procedure described in Example 1 is used to explosively clad a nickel plate to a steel plate. The stand-off distance between plates varies from The procedure of Example 1 is repeated except that the explosive detonates at 1650 meters per second and the stand-off distance between plates is 700 mils. The plate velocity is 475 meters per second and the plate impact angle 16.5 The composite is bonded over greater than 90 of the interface. The interface in this case is straight, and there is no detectable solidified melt in the bond zone although there is deformation adjacent the interface in the direction of detonation. A sample cut from the clad is cold-rolled to 97% reduction in thickness with no sign of debonding.

Examples 9-13 The general procedure described in the preceding examples is used to explosively clad titanium inch) onto Grade 1008 steel /2 inch). Grade 35-A titanium is used. The conditions and results are reported in Table II. In all examples except Example 13b, bonding is achieved over greater than 90% of the interface. The ductility of the clad composites is measured in terms of percent elongation of Z-inch gauge length specimens obtained in a tensile test (ASTM designation E8). The elongation values given in the table are an average of three tensile tests for each clad composite. All tensile specimens are taken parallel to the direction of detonation.

As is seen from Table II, the ductility of clads made at 2000 meters per second collision velocities is greater than that of clads made at collision velocities above 2500 meters per second, especially as larger stand-offs are used. It is significant that the ductility values for the 2000- meters-per-second clads are rather constant over a wide range of stand-offs, while those for the higher-velocity clads decrease as stand-off increases. Thus, operating under the conditions of the present process, i.e., at collision velocities below about 2500 meters per second, permits unifonmly desirable product properties to be obtained over wider ranges of operating conditions. The table also shows that wave amplitude and melt are sig- Table IL-TITANIUM-STEEL OLADS per second the melted areas are considerablyalargerin size.

Bond Zone Characteristics Collision Stand-Off Plate Velocity, Plate Test Example No. Velocity, mils m./see. Impact Equivalent Elongat1on,

m./sec. Angle, Type Wave-length, IL Amplitude, p Melt Thiekpercent nesS,

2, 000 45 330 9. 9 Wavy 103 8 1 32 500 45 400 0. 7 .do 254 19 1. 2 32 3, 600 45 580 9. 3 Melted layer 250 23 14.0

and waves. 2, 000 85 420 12.2 215. 17 1 34, 2, 500 85 465 11. 482 47 3. 0 29 3, 600 85 710 11. 3 468 59 11. 6 28 2,000 156 495 14.2 373 31 1 31 2, 500 156 520 12. 1 768 89 3. 1 29 3, 000 156 845 13. 4 868 122 9. 2 2, 000 250 530 15. 2 610 53 1 32 2, 500 250 565 13.0 1, 009 130 8. 2 29 3, 600 250 945 15.0 1,228 180 18. 5 2, 000 415 560 15. 5 1, 013 96 1 32 2, 500 415 600 14. 0 1, 300 167 3.6 27 600 415 1, 040 16. 5 1, 360 230 21. 8 23 80% bonded.

The shear'strength of the'titanium-to-steel' clad product made in Example 11a is determined both parallel and transverse to the direction of detonation. An average shear strength of 50,000i2000 p.s.i. is obtained for each direction. Shearing occurs in the steel backer rather than in the bond zone, however; therefore, the true shear strength of the bond zone is higher than the measured strength. In contrast to this, a titanium-to-steel clad made TABLE III Bond Zone Characteristics Cladder Metal (Thickness Backer Metal (Thickness Stand-off, Collision Example No. in inches in inches) mils Velocity, Equivalent m./sec. Type Melt Thickness,

14 Grade A Nickel (0.125).-. Copper (0.5) 156 1, 650 Wavy (762p. wave length) 1 102p. amplitude. 14a Repetition of Ex. 14 except that 2 layers of 0.125 inch nickel are clad onto the 0.5 inch copper layer simultaneously by positioning the explosive on the outside surfaces of Similar to those of Ex. 14 both nickel layers and initiating both explosive layers simultaneously. The same exp'losive loading and stand-off used in Ex. 14 are used for each N i-Cu pair in the sys em. 15* Tantalum (0.05) Grade 1008 Steel (0.5) 60 1, 900 Straight 1 16.. 304L Stainless Steel (0.06)-... 5083-0 Aluminum (0.75). 45 2, 200 1 17.- 304L Stainless Steel (0.125)... 5083-0 Aluminum (0.75)..... 45 2,100 -5 1a... 35A Titanium (0.19) 304 Stainless Steel (0.75)- 200 2, 300 1 -do -do 200 2, 800 10 19-. Grade 11 Zirconium (0.125).. A212BFBQ*** Steel (1.0) 80 2,200 1 20-- .-do 304L Stainless Steel (0.75 175 2,200 10 21-- Grade 11 Zirconium (0.1 A212BFBQ, Steel (1.0). 175 2,200 10 22. Grade 11 Zirconium (0.375)... A2I2BFBQ Steel (1.0). 300 2,300 10 Clad composite from Example 15 is reduced by of thickress bty 1:old-rolling, without tailing.

me rum-ear ous 'ee method, except in Example 14 (framing camera).

using a collision velocity of 2800 meters per second gives an average shear strength of only about 40,000 p.s.i.

Bond integrity of the clad product is also determined from the ability of the product to withstand cold-rolling. The product made in Example 11a can be reduced to 66% of its thickness by cold-rolling in a direction normal to the direction of detonation without debonding. As a comparison, a titanium-steel clad product is made under the same conditions as used in Example 11a except that the explosive has a detonation velocity of approximately 3200 meters per second. The plate velocity is 790 rn./ sec. and plate impact angle 13.8. The product is 100% bonded, the bond zone consisting of a wavy zone with pockets of melt. The wave length is 1017 amplitude 139 and the average thickness of the-melt 16 The product debonds completely after only a reduction in thickness by cold-rolling.

FIGURES 3, 3A and 3B show the influence of collision velocity on the amount of melt produced in the titanium clads of Example 11, i.e., those made at a constant stand-01f of 156 mils and nearly constant plate impact angle, but at three different collision velocities. As is seen from the photomicrographs of the figures, there is practically no melt in the bond zone at 2000 meters per second. At 2500 meters per second, melted pockets of increasing size appear in the bond zone, and at 3600 meters "Detonation velocity measured by pin Example 23 A /e-inch thick Grade 35-A titanium plate is clad explosively to a /z-inch-thick Grade 1008 steel plate by the method described in the preceding examples with the exception that the plates are arrayed initially at an angle to one another. The titanium cladder plate is tilted so that the plate edge nearest the explosive initiation end is spaced from the steel backer plate by a 250-mil standoff; and the opposite edge is spaced from the backer by an 880-mil stand-off. The angle between the cladder plate at the initiation edge and a plane parallel to the backer plate is 4. The explosive detonates at a velocity of approximately 1800 meters per second. The layer of explosive is initiated by means of a line wave generator of the kind shown in FIGURE 2B of US, Patent 2,943,571.

Initiation of the explosive layer drives the cladder plate into the hacker plate in a manner such that the plate velocity upon impact is 540 meters per second, and the angle of deflection, 'y, of the moving plate just before impact is 15.5. The collision velocity, V is determined from the relationship:

li sin 'y D sin (7+5) where D is the detonation velocity of the explosive and 6 is the initial angle between the plates. This relationship is given in the above-cited Belgian Patent 633,913 (second part of relation m). According to this determination, the collision velocity is approximately 1460 meters per second.

The clad composite is found to be metallurgically bonded over more than 90% of the interface. The interface is in the form of waves having a wave length of 1250 microns and an amplitude of 99 microns. The equivalent melt thickness is less than one micron.

We claim:

1. In the process for metallurgically bonding metal layers by propelling said layers together with an explosive, the improvement which comprises effecting collision with respect to each of said metal layers at a velocity above about 1400 meters per second but below 120% of the sonic velocity of the metal in the system having the highest sonic velocity and no greater than about the transistion collision velocity, said transition collision velocity being that velocity above which there is a substantial increase of melt with collision velocity at constant impact angle, the surfaces to.be bonded of said metal layers being disposed at an angle of less than to each other prior to detonation of said explosive, at least two of siad layers to be bonded to each other being of different metals, said metals being bonded to each other having a specific gravity of about from 2 to 17, the difference in specific gravity therebetween being no more than 9, the standoff between the layers prior to detonation of said explosive being about from 0.3 to 5.6 times the thickness of the propelled metal.

2. A process of claim 1 wherein at least two metal layers are positioned substantially parallel to each other.

3. A process of claim 2 wherein three metal layers are positioned substantially parallel to each other, a layer of explosive is positioned adjacent the outer surface of each of the two outer metal layers, and the explosive layers adjacent each of said two metal layers are detonated simultaneously.

4. A process of claim 2 wherein two layers of ditferent metals are positioned substantially parallel to each other and an explosive layer positioned adjacent the outer surface of one of said metal layers is detonated.

5. In the process for metallurgically bonding metal layers by propelling said layers together with an explosive, the improvement which comprises positioning two layers of different metals substantially parallel to each other, effecting collision with respect to said metal layers at a velocity of about from 1400 to 2500 meters per second and below of the sonic velocity of the metal in the system having the highest sonic velocity by detonation of a layer of explosive positioned adjacent the outer surface of one of said metal layers, each of said metal layers having a specific gravity of about from 4 to 17, the difference in specific gravity therebetween being no more than 9, said explosive layer having a weight of about from 0.2 to 3 times that of said metal layer to which it is adjacent and the standoff between said layers prior to detonation of said explosive being about from 0.3 to 5.6 times the thickness of said metal layer adjacent said explosive.

6. A process of claim 5 wherein said metal layers are selected from the group consisting of copper, nickel, iron, silver, titanium, zirconium, tantalum and alloys thereof.

7. A process of claim 6 wherein the collision velocity is about from 1900 to 2300 meters per second.

8. A process of claim 1 wherein the two metal layers being bonded, one consists essentially of titanium and the impact angle between said layers is about from 7 to 20.

9. A process of claim 1 wherein of two layers being bonded, one consists essentially of nickel and the impact angle between said layers is about from 4 to 18.

10. A process of claim 1 wherein said collision velocity is at least that at which a wavy interface is formed between the metal layers to be bonded on collision.

11. A process of claim 10 wherein said metal layers are selected from the group consisting of copper, nickel, iron, silver, titanium, zirconium, tantalum and alloys thereof.

12. A process of claim 11 wherein one of said layers is of steel.

References Cited UNITED STATES PATENTS 3/1966 H-oltzman et al. 29-497.5 8/1966 Popoff 29497.5 

